Conventionally, in a production site where a welding process is performed, for example, an industrial robot including a welding robot for performing welding work is introduced, and automation and manpower-saving are promoted. Here, “industrial robot” is a generic name for a configuration where a manipulator, a controller, a tool for work, and the other peripheral devices are interconnected. “Welding robot” is a generic name for a configuration where apparatuses and components such as a manipulator, a controller, a welding machine, a welding torch, and a welding electrode, and the other peripheral devices are interconnected. Recently, for improving the efficiency of the welding work, for example, for reducing the time for the welding work, a plurality of industrial robots are used for one object (hereinafter referred to as “work piece” in response to the generic name), and a plurality of industrial robots are apt to be operated simultaneously and collectively.
In such a case, the following coordinative control between robots is often used: a handling robot that grips a work piece firstly changes the attitude of the work piece to a coupling attitude that allows appropriate welding, and a welding robot operates a welding torch to perform welding in coordination with the handling robot. In such an example, it is important to control the relationship in the relative position and relative attitude (hereinafter referred to as “relationship”) between a tool for work (for example, a gripping mechanism for gripping a work piece) of the handling robot that grips the work piece and a tool for work (the tip of a welding electrode in the welding torch) of the welding robot. For example, when the robot that grips the work piece is operated manually, the control is performed so that a robot that grips the welding torch is operated while the relationship is kept. Such control is the so-called “associative movement control”, and is widespread (for example, Patent Literature 1).
Alternatively, an example is known where, one of two robots carries a tungsten inert gas (TIG) electrode, the other robot carries a filler wire, and the electrode is made close to the filler wire and is TIG-welded to it by coordination operation (for example, Patent Literature 2). In this case, the positional relationship between the TIG electrode, filler wire, and a weld line under welding is important. Therefore, Patent Literature 2 discloses the example where the operation trajectory is shifted in response to a signal from the outside while the relative position is kept, and further the relative position is finely adjusted. Such control is also a type of “associative movement control”.
In a considered method of performing the efficiency improvement such as time reduction of the welding process, two welding robots each of which has one electrode are used, and two-electrode welding is performed for one weld line.
A general welding condition for welding includes many parameters such as “welding current”, “welding voltage”, “welding speed”, “weaving method”, and “aiming position for welded joint”. Here, “aiming position for welded joint” indicates the position of the tip of the welding electrode for a welded joint and the angle of the welding electrode with respect to the welded joint.
In the welding by two welding robots, the welding result depends on the relationship between two welding robots. The relationship between two welding robots is specifically the relative position between the tips of two welding electrodes of the two welding robots and the relative attitude between the tips of two welding electrodes. In this case, in addition to “aiming position for welded joint”, “relationship” is also one of parameters constituting the welding condition. In order to perform welding for forming a desired bead with stable arcs without making two arcs generated by two welding electrodes interfere with each other, an appropriate relationship is required.
As the welding condition including many parameters, an appropriate combination is often determined by performing welding many times by try and error while each parameter is changed. The operation is referred to as “welding conditioning work”. For performing “welding conditioning work”, generally, an actual work piece to be welded is not used but a test piece formed by reproducing only the welded joint is used. In the welding by two welding robots, “relationship” is also determined through “welding conditioning work”.
The welding work for an actual work piece to be welded is performed by execution of the predetermined program by the welding robots. The welding work by the welding robots includes many sequential operations, and is performed by controlling an apparatus such as a welding machine as necessary in response to the operations. Therefore, a sequence of commands and data that indicate respective operations required for the welding work and a command and parameter that are required for controlling an apparatus such as the welding machine are registered in the program.
When the program is created, these commands, data, and parameters are stored in a storage medium such as a memory of the controller of the welding robot. The command and data indicating each operation include data indicating the coordinate and attitude for each operation. The welding robot is actually moved to the coordinate and attitude, and the program is created so as to teach the welding robot the work. This operation is referred to as “teach”. Generally, this program creating work is referred to as “teaching work”. The means of the coordinate and attitude of the welding robot is described later.
In the teaching work for the welded joint of the welding part of the work piece, the welding condition obtained by the welding conditioning work is reflected to the program. As numerical parameters such as welding current and welding voltage, of the welding condition, the values obtained by the welding conditioning work are set in the program. Thus, the welding obtained by the welding conditioning work can be relatively easily reproduced. While, regarding “relationship” during welding, the relationship between two robots in the target welding part of the work piece is reproduced and taught by actually operating two welding robots for each operation during the actual welding.
In a considered method for teaching the relationship, “aiming position for welded joint” of one robot is firstly reproduced, and then “relationship” is reproduced by operating the other. Another method may be used where “relationship” is reproduced near the welded joint and then “aiming position for welded joint” is reproduced by operating both robots while the relationship is kept (here, “associative movement control” is used). Among them, as a considered method for reproducing the relationship, the coordinate and attitude in the coordinate system of each welding robot during the welding conditioning work are noted, and the coordinate and attitude are reproduced referring to the note during teaching of the target welding part of the actual work piece. Generally, at that time, the position in the coordinate system of the welding robot is completely different from that in the welding conditioning work, and the direction of the weld line is not always the same. Therefore, the noted values of the coordinate and attitude are converted into the present coordinate and attitude, and the relationship is reproduced with the welding robot. This operation is actually extremely troublesome. The controller of a usual welding robot has a function of displaying the coordinate and attitude of the control point, so that the coordinate and attitude in the coordinate system of each welding robot can be obtained using the function. Generally, the control point is disposed at the tip of the welding electrode.
Once the relationship is established, “associative movement control” where one robot is moved in response to the operation of the other robot while the relationship is established becomes a useful function. The teaching of the welding part is performed by driving “associative movement control” of two welding robots. However, at the start of the control, it is an issue how “relationship” obtained in welding conditioning work is reproduced and established. How the relationship can be easily established before “associative movement control” is a common issue for not only the welding robots but also all industrial robots employing “associative movement control”.
Further, when a work piece to be welded has a plurality of weld lines and a plurality of welded joints must be welded, the welding conditioning work is performed for each welded joint. As a result, a plurality of “relationships” is obtained. In the teaching work, it is required to select one of the plurality of relationships correspondingly to the welded joint for each welding part. In this case, the troublesome work must be performed a plurality of times. Once the relationship is established, “associative movement control” where one robot is moved in response to the operation of the other robot while the relationship is established becomes a useful function. However, at the start of the control, it is an issue how one “relationship” is reproduced and established from the plurality of relationships obtained in welding conditioning work. This issue is also a common issue for not only the welding robots but also all industrial robots employing “associative movement control”.